Impact of bendiocarb 80% WP indoor residual spraying on insecticide resistance status of Anopheles arabiensis
Long term and wide use of indoor residual sprays augments the selection of insecticide resistance genes. The development of insecticide resistance in an insect population depends up on the volume and frequency of sprays against them and the inherent characteristics of the insect species. However, despite its use for decades, the effect of residual sprays on the status of insecticide resistance of malaria vectors is unknown in Ethiopia. The objective of this study was to assess the effect of bendiocarb 80% WP indoor residual spraying on insecticide resistance status of An. arabiensis in Bahir Dar Zuria District, Northwest Ethiopia. Susceptibility of An. arabiensis was examined against different insecticides using 2-3-day old female mosquitoes following WHO insecticide susceptibility test procedures. Test results were calculated according to WHO bioassay test protocol. Chi-square test was used to determine the significance level of differences between years and study sites. Susceptibility of An. arabiensis to fenitrothion, pirimiphosmethyl and propoxur was 100% in both study villages for three successive years. Resistance to bendiocarb was suspected after two years (2015) in Andassa, but not in Tikurit. Mortality and knock down due to DDT significantly increased from 2013 to 2015 at Tikurit (knock down: χ2 = 117.9, P<.0001 and mortality: χ2 = 66.3, P<.0001; due to deltamethrin, knock down: χ2 = 7.3, P=.004 and mortality: χ2 = 37.8, P<.0001). The same was true at Andassa (due to DDT, knock down: χ2 = 198.7, P<.0001 and mortality: χ2 = 82.9, P<.0001; due to deltamethrin, knock down: χ2 = 26.1, P<.0001 and mortality: χ2 = 48.2, P<.0001). Bendiocarb was effective against the An. arabiensis for two years under bendiocarb IRS operation so that alternative insecticides with different mode of action should be replaced every two to three years to prolong its efficacy.